Alternative to nested Con statements in python

Question

I have a nested con statement that I'd like to put into a script, as it's hard to follow in its current form. The raster it produces is incorrect, so it'd be easier to debug in a script.

The current set of statements looks like this:

EWR_2015 = Con("ministerial_wetlands">0," ministerial_wetlands ",
(Con("non_ministerial_wetlands ">0,("WTE_using_2001_min"-0.25),
(Con(("nat_veg_raster" >0) & ("dtgw_2001_min" <= 3) ,    
("WTE_using_2001_min"-0.75), 
(Con(("nat_veg_raster ">0) & (("dtgw_2001_min ")>3 & ("dtgw_2001_min " <= 6)) , ("WTE_using_2001_min"-1.0), 
(Con(("nat_veg_raster ">0) & (("dtgw_2001_min " > 6) & ("dtgw_2001_min "<= 10)),(" WTE_using_2001_min "-1.25)
)))))))))

I would like to use a series of if/ elif statements in Python to do a similar thing.

I tried this for the first statement:

ministerial_wetlands = Raster("ministerial_wetlands")
if ministerial_wetlands>0:
    outRaster = Raster(ministerial_wetlands)

This gives the following error message: ValueError: The truth value of a raster is ambiguous. Invalid use of raster with Boolean operator or function. Check the use of parentheses where applicable.

Not sure where to go from here.

Answer 1

Not sure if this helps, but I have a script with many nested Con statements, and I find just using indentation helps. For example:

EWR_2015 = Con(
    "ministerial_wetlands" > 0,
    " ministerial_wetlands ",
    Con(
        "non_ministerial_wetlands " > 0,
        "WTE_using_2001_min" - 0.25,
        Con(
            "nat_veg_raster" > 0 & "dtgw_2001_min" <= 3,
            "WTE_using_2001_min" - 0.75, 
            Con(
                "nat_veg_raster " > 0 & ("dtgw_2001_min " > 3 & "dtgw_2001_min " <= 6),
                "WTE_using_2001_min" - 1.0,
                Con(
                    "nat_veg_raster " > 0 & ("dtgw_2001_min " > 6 & "dtgw_2001_min " <= 10),
                    " WTE_using_2001_min " - 1.25
                )
            )
        )
    )
)

It does take up more space, but it's worth the extra legibility.

Answer 2

You can split it up into more readable/debug-able chunks using variables.

con_1 = Con(
    "nat_veg_raster " > 0 & ("dtgw_2001_min " > 6 & "dtgw_2001_min " <= 10),
    " WTE_using_2001_min " - 1.25
)

con_2 = Con(
    "nat_veg_raster " > 0 & ("dtgw_2001_min " > 3 & "dtgw_2001_min " <= 6),
    "WTE_using_2001_min" - 1.0,
    con_1
)

con_3 = Con(
    "nat_veg_raster" > 0 & "dtgw_2001_min" <= 3,
    "WTE_using_2001_min" - 0.75, 
    con_2
)

con_4 = Con(
    "non_ministerial_wetlands " > 0,
    "WTE_using_2001_min" - 0.25,
    con_3
)

EWR_2015 = Con(
    "ministerial_wetlands" > 0,
    " ministerial_wetlands ",
    con_4
)